View Full Version : A question about black holes
2005-Feb-14, 02:50 PM
Hi.. If anyone could answer a quick question.
I have a very basic understanding of black holes which goes as follows. A massive star collapses in on itself creating a black hole. This black hole is so powerful that its gravity sucks everything, all matter and even light into its centre past its event horizon and onto a singularity.
Now what i dont understand is that if a black hole sucks everything into it does this mean that the universe being eaten by these black holes, so that eventually, all matter in the entire universe is eaten, leaving nothing?
Or is it that a black hole can only eat a certain amount and has a limited lifespan... if this is the case, then what happens to the black hole and all the matter it has eaten?
Or is it the case that the Universe is expanding quicker than the black holes can eat it? So there is always more universe being created to counter the universe being eaten?
As you can see, my understanding of these things is very limited... but any help would be appreciated!!
2005-Feb-14, 03:46 PM
Darrius, A black hole also emits paticles indirectly, thus losing mass. A particle and antiparticle are created in the region outside the black hole, one of which is emmited by the hole. Thus, a black hole loses mass, and eventually ends. How that happens, is not known.
Why don't you read " A breif history of time" by Stephen Hawking? It's a good source of info about black holes.
2005-Feb-15, 11:51 AM
Another point about black holes is that they are generally small targets- if something comes close to a black hole, it doesn't generally hit it head on, but instead goes into a hyperbolic orbit around it, which means that the object would escape on the other side.
However large objects are often torn apart by tidal forces at the closest approach to the black hole, and a fraction of the debris goes into orbit (forming an accretion disc), or even falls directly into the hole.
About 5% of the mass encountered by a black hole is eaten by the hole; the rest is flung away.
2005-Feb-15, 12:59 PM
Here you are Darrrius, take a look at
*This (http://www.gothosenterprises.com/black_holes/forming_black_holes.html) link to discover everything you need to know about the formation of black holes.
*This (http://www.gothosenterprises.com/black_holes/black_holes_types.html) is about the different types of black holes.
*Here (http://www.gothosenterprises.com/black_holes/outside_black_holes.html) you can find out what we interprite is on the outside of a black hole and here (http://www.gothosenterprises.com/black_holes/inside_black_holes.html) about the inside.
*This link (http://www.gothosenterprises.com/black_holes/finding_black_holes.html) will explain the basics of not being able to "find" black holes as such.
They are really great and detailed links. I would read Stephen Hawkin's Breif History of time as Rahul has indicated - it's a great book, I know from experience.
Generally speaking, people would identify a black hole as being a region in space where gravity is so strong that not even light can escape from it. The black holes in our Milky Way are thought to be formed when stars more than ten times as massive as our Sun end their lives in a supernova explosion. There is also evidence indicating that supermassive black holes (more massive than ten billion Suns) exist in the centers of some galaxies. You know all of this already, so, there we go.
Hope this helps
2005-Feb-15, 02:44 PM
Thanks ever so much guys!! I've got a lot of reading to do... thanks for the links Rigel.... Thats exactly what I was looking for!!
2005-Feb-15, 02:52 PM
THe theory that black holes were eating everything, prompted some scientists to start looking for white holes. (Emitting mass and light) But no evidence has been found to back this up....
2005-Mar-08, 11:17 AM
in my opinion the black holes are the mines of future stars and galaxies, black hole material itself is a raw material for forming new star.
2005-Mar-09, 03:35 PM
It's a misconception that black holes eat everything up. If the sun turned into a black hole (which it can't do) then the Earth would continue happily circulating around it in the same orbit it does now virtually forever. We'd get a little cold though :)
The only things they eat up are whatever comes close enough to be affected by its gravity, the same way the sun can swallow a comet that gets too close.
2005-Mar-09, 04:51 PM
I suggest also the following books:
* Black Holes from Jean-Pierre Luminet (Cambridge University Press)
* Black Holes & Time Warps from Kip Thorne (WW Norton)
2005-Mar-09, 05:22 PM
One more important thing. Gravity obeys the inverse square law, which states that as the distance from the object doubles the strength of the gravity decrease to 1/4. So a black hole can pull in, through its immense gravity, anything that is or comes close, but the further away you pass the less you would feel the pull of the black holes gravity. It isn't very far away that the gravity of all the other stuff in the universe cancels out the pull of the black hole.
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